java.sun.com/j2se/1.3/docs/api/java/io/Serializable.html
Classes that do not implement this interface will not have any of their state serialized or deserialized. All subtypes of a serializable class are themselves serializable. The serialization interface has no methods or fields and serves only to identify the semantics of being serializable. To allow subtypes of non-serializable classes to be serialized, the subtype may assume responsibility for saving and restoring the state of the supertype's public, protected, and (if accessible) package fields. The subtype may assume this responsibility only if the class it extends has an accessible no-arg constructor to initialize the class's state. It is an error to declare a class Serializable in this case. During deserialization, the fields of non-serializable classes will be initialized using the public or protected no-arg constructor of the class. A no-arg constructor must be accessible to the subclass that is serializable. The fields of serializable subclasses will be restored from the stream. When traversing a graph, an object may be encountered that does not support the Serializable interface. In this case the NotSerializableException will be thrown and will identify the class of the non-serializable object. ObjectInputStream in) throws IOException, ClassNotFoundException; The writeObject method is responsible for writing the state of the object for its particular class so that the corresponding readObject method can restore it. The method does not need to concern itself with the state belonging to its superclasses or subclasses. State is saved by writing the individual fields to the ObjectOutputStream using the writeObject method or by using the methods for primitive data types supported by DataOutput. The readObject method is responsible for reading from the stream and restoring the classes fields. The defaultReadObject method uses information in the stream to assign the fields of the object saved in the stream with the correspondingly named fields in the current object. This handles the case when the class has evolved to add new fields. The method does not need to concern itself with the state belonging to its superclasses or subclasses. State is saved by writing the individual fields to the ObjectOutputStream using the writeObject method or by using the methods for primitive data types supported by DataOutput. Serializable classes that need to designate an alternative object to be used when writing an object to the stream should implement this special method with the exact signature: ANY-ACCESS-MODIFIER Object writeReplace() throws ObjectStreamException; This writeReplace method is invoked by serialization if the method exists and it would be accessible from a method defined within the class of the object being serialized. Thus, the method can have private, protected and package-private access. Subclass access to this method follows java accessibility rules. Classes that need to designate a replacement when an instance of it is read from the stream should implement this special method with the exact signatute. ANY-ACCESS-MODIFIER Object readResolve() throws ObjectStreamException; This readResolve method follows the same invocation rules and accessibility rules as writeReplace. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples. Java, Java 2D, and JDBC are trademarks or registered trademarks of Sun Microsystems, Inc.
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